Graceful handling of :topic_not_found

[technomage]

We have circumstances where a topic is deleted and recreated, it would be nice to be able to gracefully handle the :topic_not_found error in those cases. Allowing for that in the consumer and an optional callback to ignore would be sufficient. Let me know if this would be acceptable and I can do a pull request.

[joshuawscott]

Is this in the GenConsumer and related consumer group functionality, or is this the lower level consumer?

[IanVaughan]

I've spotted this as well, and think I might have a solution as part of #298, in which it can be setup to retry attempting to connect to a topic until present.

[technomage]

I ended up using a module that delays the retry by monitoring the consumer rather than directly placing it in the supervisor tree. This is working for me.